Photographic media and process for producing same



United States Patent 3,219,452 PHOTOGRAPl-HC MEDLA AND PROCESS FORPRODUCING SAME Edward Hartouni, Westwood, Mass, assignor, by mesneassignments, to Technical Operations, Incorporated, a corporation ofDelaware No Drawing. Filed Dec. 11, 1962, Ser. No. 243,740 23 Claims.'(Cl. 96108) This invention relates to photography, and moreparticularly to novel sensitized photographic media and processes forproducing same.

Photographic media formed of a layer of microcrystalline, substantiallybinder-free silver halide on a suitable substrate, and a process formanufacturing such media by vacuum evaporation techniques are disclosedin French Patent No. 1,267,623, granted June 12, 1961, to TechnicalOperations, Incorporated. Media of this type can be distinguished fromconventional emulsion type photographic film and other photographicmedia not only by their structure and method of manufacture, but alsofor some purposes by their high acutance, high resolution, and quickdevelopability.

Such media may be photographically sensitized by treatment of thesurface of the microcrystalline binder-free silver halide layer.

Media of this type are especially useful, for example, in image transferprocesses, because the image developed therein is not masked by binderand can be transferred by adhesion of the surface of a developed silverimage to the surface of a receiving sheet. In transfer processes, it isoften desirable to have the transferred image in positive form i.e.having image densities which are approximately inversely proportional tothe intensity of the radi ation which formed the latent image. With asurface sensitized medium, transfer usually removes substantially all ofthe image, hence but only one transfer of that image can generally bemade.

The present invention is directed to improvements in the sensitizationof microcrystalline binder-free silver halide photographic media, andhas for its principal object to provide novel bulk sensitizedphotographic media of this type and methods for making the same.

More specific objects of the present invention are to provide such amethod in which both the photosensitive silver halide and thesensitizing material are codeposited on a substrate such as by vacuumdeposition; to provide a method of producing a substantially binder-freelayer of particulate silver halide having sensitizing materialsubstantially homogeneously distributed therein; to provide novelsensitized photographic media; to provide a medium which is sensitizedto produce a direct positive image upon short exposures and normaldevelopment; to provide a medium which is sensitized to produce aprint-out effect; to provide a direct positive-image producing mediumwherein the sensitizer is selected from the group consisting of iron,tin, indium and tellurium; and to provide a method of forming in asimple evaporation process, a sensitized photographic medium.

Other objects of the present invention will in part be obvious and willin part appear hereinafter. The invention accordingly comprises theprocess involving the several steps and the relation and order of one ormore of such steps with respect to each of the others, and the productsand compositions possessing the features, properties and relation ofelements which are exemplified in the following detailed disclosure, andthe scope of the application of which will be indicated in the claims.For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed 3,219,452 iatentedNov. 23, 1965 description of the invention and certain exemplaryembodiments thereof.

The present invention is intended to form in one processmicrocrystalline binder-free silver halide photographic media which arebulk sensitized. Certain media of this type are developable to formdirect positive images following brief exposure, hence are termed directpositive media. Other media of this type, upon exposure, exhibit aprint-out effect i.e. the formation of a visible silver image withoutdevelopment.

While not being limited to any particular theory, it is believed thatthe sensitization phenomena of the present invention are due, notprimarily to surface effects as appears to be true in surfacesensitization (of microcrystals in either binder-free form or emulsionsuspension) but probably largely to distortions introduced into thecrystalline lattices of the silver halide microcrystals themselves bythe sensitizer or to internal chemical reactions between the sensitizerand the silver halide photolysis products.

Photographic media according to the present invention may be prepared byvacuum evaporation techniques similar to those described in theaforesaid French Patent No. 1,267,623. A basic machine of the kinduseful to form such media by vacuum evaporation is illustrated and described in the book, Vacuum Deposition of Thin Films by L. Holland,published by John Wiley & Sons, New York City, 1948, pp. 7-8. Vacuumcoating apparatus of this type is well known and usually comprises anevacuatable container, such as a bell jar, and means for evacuating thelatter to an ambient pressure which is preferably less thanapproximately 1 l0- mm. of Hg. The latter appears to be the maximumpressure at which reasonably desirable layer formation can be achieved.Included within the bell jar is a crucible or boat which is intended tocarry the material which is to be evaporated. Means for heating the boatare usually included, and in one form of the apparatus the boat is madeof, for instance, tungsten provided with leads to a source of electricalpower so that the filament can be heated electrically. By this methodthe temperature of the evaporating material can be readily controlled.In other known forms of vacuum evaporation apparatus, the startingmaterial may be heated by electrical induction, for example. Theapparatus also includes means for holding substrate material, such as asupport sheet, at a predetermined location within the bell jar whereinpreferably one surface of the substrate faces the boat, thus insuringthat the stream of vapor from the evaporating material in the boat willstrike the substrate surface and condense thereon to form a film orlayer according to the well known principles of evaporation techniques.It is desired to keep the silver-halide layer thus formed within athickness range of about 0.1 to 0.5 micron inasmuch as optimumphotographic param eters such as gamma, density, and speed are foundwithin this range.

In one method of using this apparatus, a quantity of silver halide, e.g.of purity of 99.99% or better, and a quantity of the sensi'tizermaterial or dopant are placed within the container, for example at afirst location, and a suitable substrate sheet is placed within thecontainer at a second location displaced from the first location. Thecontainer is pumped down to achieve an operating pressure, and thesilver halide and the dopant are brought to a temperature at whichevaporation, at least of the silver halide, will occur. The resultingvapor in which dopant is commingled, as by evaporation thereof or byentrapment, is a sensitizer-doped silver halide which is then condensedupon the substrate surface to form the product.

In another form of the foregoing process, the silver halide is firstprepared in high purity form, brought to 'to the support, and otherreasons. such subbing layers on base materials are well known I and neednot be described here.

a molten state, and the desired quantity of sensitizerdopant isintroduced into the molten .silver halide, as by mixing or reactingdirectly with the latter. The doped silver halide is then cooled and isready for use in the vacuum evaporator by, for example, reheating to amolten state in a single crucible. This, provides a precisely knownpre-evaporation composition for the doped silver halide.

.In yet another form of the method of the invention, the high puritysilver halide is placed in a single crucible, rendered molten under therequisite reduced pressure, and the dopant, for instance in the form ofan elemental metal or a salt is placed directly into the molten silver'salt at the beginning of or during the evaporation process.Alternatively it has been foundthat suspending a dopant metal in thevapor stream from molten silver halide being evaporated under reducedpressure will also result in introducing the dopant, probably as ahalide due to reaction of the metal with the silver halide vapor, intothe final evaporated film.

Yet another method of achieving the doped product is to employ apparatusof the type disclosed in US. Patent No. 2,938,816, Karl George Gunther,for simultaneous vacuum evaporation or coevaporation, of two or morematerials from a corresponding number of crucibles, each of which maythen be separately temperature controlled, to provide a commingled vaporfrom which is deposited a thin layer of doped photographic material ofthe type 'hereinbefore described.

Among the silver halides which are useful in evaporation processes toform the media of the present invention are silver bromide, silverchloride and silver iodobromide.

Exemplary support or substrate materials upon which the "doped film isdeposited include many diverse materials,

other polyesters, polyamides and the like; and cellulose esters such ascellulose'acetate, cellulose propionate and the like.

.In any of the above methods, the thickness of the doped silver halidelayer is readily controlled as by adjustment of the evaporationtemperature, the evaporation time and the distance between the silverhalide source and the substrate, or any of them. The layer thus providedexhibits a density which appears quite close, i.e.

within approximately to that of a solid silver halide macrocrystal.

The base or substrate materials may be transparent, translucent oropaque to radiation actinic to the silver halide, and may be useddirectly to provide a condensation surface or may be coated with asubbing layer. The subbing layer may be provided for several purposes,eg

to alter support opacity, to change support reflectivity, to modifyadherence of the silver-halide-sensitized layer Methods for coating Asmaterials for sensitization doping of microcrystalline binder-freesilver halide photographic media during formation of the latter byevaporation we have found many metallic substances and salts thereofwhich are useful.

For example, it appears that iron, tin, indium, tellurium,

ferred for various reasons.

For example, the use of dopants such as iron, tin,

indium or tellurium will provide a sensitized photographic medium which,upon relatively brief exposure to ordinary light intensities, andordinary development, is found to yield a direct positive image. It isbelieved that these are but some of the elements which are useful asmaterials for sensitization doping during vacuum evaporation of silverhalides to provide direct-positive media.

The use of a dopant such as lead, for example in the form of the halidesalt, will provide a photographic medium which, upon relatively briefexposure to actinic radiation, is found to yield a strong print-outeffect.

The methods of the present invention, and the products achieved thereby,may be illustrated in the following examples.

Example 1 A support sheet of polyethylene terephthalate having a subbinglayer thereon for the purpose of improving adhesion characteristics,such as material suitable for the application thereto of a photographicemulsion and sold under the trade name of Cronar by E. I. du Pont deNemours Co., is placed in the evacuatable container of a vacuumdeposition apparatus of the type described above. Six grams of highpurity AgBr is placed in a tungsten boat also located in the containerand spaced 'several inches, for instance about 3 /2 inches, from thesubbed surface of the support sheet. A sample, about 4 inches long ofapproximately #18 gauge, of very pure iron is suspended about inch abovethe tungsten boat. The container is evacuated to a pressure of about 5 Xl0 mm. of Hg and the boat heated electrically to a temperature ofapproximately 600:20 C. to bring the silver halide to a molten state andcause evaporation thereof for a sufiicient time to form a layer ofphotosensitive material about 0.25 micron thick on the subbed surface ofthe support sheet. The latter, being essentially vacuuminsulated fromthe boat is maintained at an equilibrium temperature of approximately5060 C. The iron wire, being suspended in the stream of silver halidevapor between the boat to the support sheet, will be corroded apparentlyby reaction with the vapor thereby providing a mixed vapor which forms aphotosensitive layer doped with iron in some form, probably as thebromide.

The photographic medium thus formed i removed from the vacuum depositionapparatus and exposed in a moving wedge sensitometer (using a standardstep wedge made by Eastman Kodak Co., and a light source corrected to5600K) over 0.1 second intervals between 0.1 and 0.4 second. The exposedmedium is then developed by immersion for 30 seconds at 25 C. in asolution made up as follows:

Gelatin, 1.25 g. Water to make 250 cc.

These are mixed by adding equal quantities of solution B to solution Aand then of solution C to the mixture of solutions A and B.

Sensit-ometric results indicate that the average speed of thissensitized medium is increased by about one and a half orders ofmagnitude over unsensitized evaporated AgBr film made in the sameapparatus with similar parameters. Also, all of the images achieved upondevelopment are direct positive images, the maximum den sity being about2.

Example 2 0.032 g. of high purity iron, in wire form, laid directly onthe surface of the silver halide; after the latter is raised to atemperature of approximately 625 C. under an ambient pressure ofapproximately 5 X" mm. of Hg, a reaction will be observed between thewire and molten silver bromide. Evaporation is continued until a dopedsilver halide layer having a thickness of between 0.1 and 0.5 micron issubstantially uniformly deposited upon a substrate. The resultingsensitized medium yields sensitometric results quite similar to those ofExample 1.

Example 3 The experiment described in Example 1 is repeated, however,using baryta-coated paper as the support material. Again the resultsindicate substantial increase in film speed and the production of apositive image upon similar exposure and development.

Example 4 A sample of 6 g. of high purity AgBr is placed in the boat ofthe apparatus of Example 1, and 0.1 g. of indium metal is dropped intothe AgBr when the latter is approximately at 575 C. under the samereduced pressure as in Example 1. The resulting evaporated layer ofmicrocrystalline silver bromide doped in this manner with indium in someform, also yields, upon similar exposure and development, a directpositive image.

Example 5 The experiment of Example 4 is repeated employing metallic tininstead of indium metal. Substantially the same results are obtained. Inboth Example 4 and Example 5, a boiling reaction between the moltensilver bromide and the dopant will be observed. Since both reactions areexothermic, the exact local temperature conditions at the surface ofsilver bromide are uncertain.

Example 6 In the apparatus of Example 1, a pre-evaporation mix of 0.05gram of lead bromide and 5 grams of AgBr is placed in the tungsten boat.The latter is spaced about 2 /2 inches from the surface of abaryta-coated, paper support sheet. The mix is raised to a temperatureof approximately 625 C. at an ambient pressure of about 5X 10- mm. ofHg, and allowed to evaporate for a time sufficient to form aphotographic medium comprising a doped silver halide layer of about 0.3micron in thickness deposited on the baryta surface.

The sensitized medium is then surface treated by immersion in a solutionformed of 10 milligrams of ammonium chloroiridite and 10 milligrams ofsodium aurous thiosulfate per liter of water, in order to increase thesurface speed of the medium. The treated medium is then shaken andallowed to air dry.

Sensitized media, treated with the gold iridite solution or untreated,upon exposure in the sensitometer of Example 1 for 0.1 sec. will bothshow marked print-out effects. The print-out effect in both instancesmay be preserved simply by fixing the media in known fixes.

Since certain changes may be made in the above processes and productswithout departing from the scope of the invention herein involved it isintended that all matter contained in the above description shall beinterpreted in an illustrative and not in a limiting sense.

What is claimed is:

1. A method of producing a bulk sensitized photographic mediumcomprising the steps of placing in an evacuatable region a quantity ofsilver halide, placing a support surface at a predetermined distancefrom said halide in said region, locating between said halide and saidsupport surface a quantity of a material which is reactable with vaporsof said silver halide to form a sensitizing material, evacuating saidregion, heating said halide to above its melting point, and condensingthe vapor passing from said halide and including that passing across andreacting with said material to form on said support surface amicrocrystalline binder-free layer of silver halide substantiallyuniformly doped with said material.

2. A method as set forth in claim 1, wherein said material is selectedfrom the group consisting of iron, indium, tellurium, tin and lead.

3. A method as set forth in claim 1, wherein said region is evacuated toa pressure below approximately 1 10'- mm.'of Hg.

4. A method as set forth in claim 1, wherein said material is in theform of a wire.

5. A bulk sensitized direct positive photographic medium comprising asubstrate supporting a substantially homogeneous binder-freemicrocrystalline layer of vapor deposited silver halide having amaterial uniformly incorporated therein selected from the groupconsisting of halides of iron, indium, tellurium, and tin.

6. A medium as defined in claim 5 wherein said layer is of predeterminedthickness within the range of approximately 0.1 to 0.5 micron.

7. A medium as set forth in claim 5, material is iron halide.

8. A medium as set forth in claim 5, material is indium halide.

9. A medium as set forth in claim 5, material is tellurium halide.

10. A medium as set forth in claim 5, material is tin halide.

11. A medium as set forth in claim 5, wherein said silver halideincludes silver bromide.

12. Method of producing a bulk sensitized direct positive photographicmedium comprising vaporizing a silver halide and a sensitizer materialin an ambient atmosphere of less than approximately 1 l0 mm. of Hg toform a silver halide vapor doped with said sensitizer material, saidsensitizer material being chosen from the group con sisting of iron,indium, tellurium, tin, and compounds thereof, and condensing the dopedvapor onto a support to form a thin layer of binder-freemicrocrystalline doped silver halide.

13. A method as set forth in claim 12, wherein said sensitizer materialcontains iron.

14. A method as set forth in claim 12, wherein said sensitizer materialcontains indium.

15. A method as set forth in claim 12, wherein said sensitizer materialcontains tellurium.

16. A method as set forth in claim 12, wherein said sensitizer materialcontains tin.

17. A method as set forth in claim 12, wherein said silver halide andsensitizer material are vaporized by being heated in separate vessels.

18. A method as set forth in claim 12, wherein said silver halideincludes silver bromide.

19. A method of producing a bulk sensitized print-out photographicmedium comprising vaporizing a silver halide and a sensitizer materialin an ambient atmosphere of less than approximately 1 10 mm. of Hg toform a silver halide vapor doped with said sensitizer material, saidsensitizer material being chosen from the group consisting of lead andcompounds thereof, and condensing the doped vapor onto a support to forma thin layer of binder-free microcrystalline doped silver halide.

20. A method as set forth in claim 19, wherein the silver halideincludes silver bromide.

21. A method as set forth in claim 19, wherein said silver halide andsensitizer material are vaporized by being heated in separate vessels.

22. A bulk sensitized print-out photographic medium comprising asubstrate supporting a substantially homogeneous binder-freemicrocrystalline layer of vapor deposited silver halide having leadhalide uniformly incorporated therein.

wherein said wherein said wherein said wherein said 7 '8 23. Amediurn'as set forth in claim 22, wherein said Goldberg et al.: A.D. No;264,061 (Report No. TOB silver halide includes silver bromide. 61-37),August 1961. Luckey: Journal Physical Chemistry, vol. 57, pp. 79 1-References Cited by the Examiner 9% %1- 1 A N 2 7 O uVa e et a.: .D. 0.2O, 28 Report No. T -B FOREIGN PATENTS 5 5941) July 1959 1 2 7 23 19 1France. Moser et al.: Journal Physics and Chemistry of Solids,

vol. 9, pp. 217-234, 1959. OTHER REFERENCES Tutihasi: Physical Review,vol. 105, .pp. 882-884, 1957.

1O p g ri eg 211l9g6liournal V Photographic Science, vol. 4, NORMAN G.TORCHIN Primary Examiner.

Evans et 211.: Journal Photographic Science, Vol. 3, ALVIN E.TANENHOLTZ, J. T. BROWN, pp. 73-87, 1955. Assistant Examiners.

1. A METHOD OF PRODUCING A BULK SENSITIZED PHOTOGRAPHIC MEDIUMCOMPRISING THE STEPS OF PLACING IN AN EVACUATABLE REGION A QUANTITY OFSILVER HALIDE, PLACING A SUPPORT SURFACE AT A PREDETERMINED DISTANCEFROM SAID HALIDE IN SAID REGION, LOCATING BETWEEN SAID HALIDE AND SAIDSUPPORT SURFACE A QUANTITY OF A MATERIAL WHICH IS REACTABLE WITH VAPORSOF SAID SILVER HALIDE TO FORM A SENSITIZING MATERIAL, EVACUATING SAIDREGION, HEATING SAID HALIDE TO ABOVE ITS MELTING POINT, AND CONDENSINGTHE VAPOR PASSING FROM SAID HALIDE AND INCLUDING THAT PASSING ACROSS ANDREACTING WITH SAID MATERIAL TO FORM ON SAID SUPPORT SURFACE AMICROCRYSTALLING BINDER-FREE LAYER OF SILVER HALIDE SUBSTANTAILLYUNIFORMLY DOPED WITH SAID MATERIAL.